1. Field of the Invention
The present invention relates to a combined vehicle brake which has a hydraulically actuable service brake and an electromechanically actuable parking brake device, a hydraulic service pressure space being delimited in a brake housing by a brake piston which can be acted upon by hydraulic pressure medium in order to execute service braking operations, so that the brake piston can be actuated along a piston longitudinal axis in order to achieve a braking action, and a parking brake device acting upon the brake piston by means of a gear, in that the gear converts the rotational movement of an electromechanical actuator into a translational movement and causes an actuation of the brake piston in order to execute parking braking operations and holds the said brake piston in the actuated position, the gear having a threaded spindle and a threaded nut which are in contact with one another via a plurality of rolling bodies.
2. Description of the Related Art
A hydraulic vehicle brake of this type with an electrically actuable parking brake device is known, for example, from DE 101 50 803 B4, which is incorporated by reference. In the known vehicle brake, a gear is provided, which, on the operative principle of a threaded-nut/spindle arrangement, converts the rotational movement of the electric motor into a longitudinal movement of the brake piston in order to achieve a parking force. According to an exemplary embodiment, this gear unit is designed as what is known as a “spindle/ball recirculation bush arrangement” which is also referred to as a ball screw or ball recirculation spindle. These ball screws have a threaded spindle and a threaded nut which are in contact with one another via a plurality of rolling bodies.
A screw nut with a rolling-body arrangement, without what is known as ball recirculation, is known from German utility model DE 76 40 810 U, which is incorporated by reference. The disadvantage of this arrangement is that, when the arrangement is actuated, the rolling bodies are pressed against one another and friction is generated which adversely influences the efficiency of the arrangement. An object of the present invention, therefore, is to improve a combined parking brake of the generic type mentioned in the introduction, to the effect that the efficiency is increased.